Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$70.32	11.322%	$78.2816	$78.28	$78.30	$78.30
Purchase #2	$214.32	6.139%	$227.4771	$227.48	$227.50	$227.50
Purchase #3	$88.90	9.407%	$97.2628	$97.26	$97.25	$97.30
Purchase #4	$130.26	9.223%	$142.2739	$142.27	$142.25	$142.30
Purchase #5	$71.74	10.662%	$79.3889	$79.39	$79.40	$79.40
Purchase #6	$35.72	12.593%	$40.2182	$40.22	$40.20	$40.20
Purchase #7	$110.87	8.490%	$120.2829	$120.28	$120.30	$120.30
7 purchase totals =	$722.13		$785.1854	$785.18	$785.20	$785.30